1. Lab 5 Conductivity of Aqueous Solutions 1

2. Learning Outcomes To calibrate a conductometer. To use a conductometer to determine conductivity of various known and unknown solutions To use a conductometer to determine total dissolved solids of known and unknown solutions To estimate the arithmatic relation between T.D.S. and conductivity 2

3. Electrical conductance: is a measure of a material's ability to conduct an electric current. Good Conductors have high conductance. Conductance, G is measured in Siemens (S). It is the reverse of resistance. 3

4. Conductivity  it's a material property rather than a component property.  So you talk about the conductivity of the element Copper but the conductance of this piece of copper wire. A piece of wire has a high conductance if it's short and fat.  So the conductance of a piece of wire depends on 1.what it's made from (the conductivity, σ) 2.how long it is (the length, l; the longer the wire the lower the conductance) 3.its cross-sectional area (area, A; the bigger the area, the higher the conductance. It's normally represented by σ σ = Gl/A, the units for which are Ѕm/m 2 =S/m. 4 Temperature probe

5. T otal D issolved S olids The conductivity of a solution of water is highly dependent on its concentration of dissolved salts and sometimes other chemical species which tend to ionize in solution. Measurement of conductivity is a method to determine the total amount of dissolved solids (T.D.S) in a liquid (water). 5 S cm -1 5.5 ×10 -6 S cm -1 Seawater vsDeionized water 5

6. Application of T.D.S.  study of water quality for streams, rivers and lakes.  an indication of characteristics of drinking water. Measurement of T.D.S. Gravimetry and Electrical Conductivity. TDS is calculated by converting the EC by a factor of [0.5 to 1.0] times the EC. T.D.S = 0.6 X EC OUR SETTINGS (T.D.S/EC = 0.6) 6

7. Calibration of the conductivity meter K cell =  / G G: conductance of the cell containing the reference solution. (S)  : conductivity of the reference solution. (S/m) K cell : Cell constant, unit: m -1.  Aqueous solutions of potassium chloride are known as possessing sufficiently accurate conductivity to be used for reference purpose. 7

8. Guidelines for using conductivity meter 1.no particulate matter is suspended in the solution under investigation. If necessary filter. 2.Ensure no air bubbles are trapped in the cell area between the plates. 3.Ensure the cell plates are completely immersed in the solution under test. 4.Thoroughly rinse the cell plates in deionized water after (each) use, and for short term storage immerse the cell in deionized water. 5.Do not attempt to clean the cell plates by any other means than rinsing with deionized water. 6.Ensure no salt deposits or particulate matter are allowed to build up around the cell plates or on the probe body as this may produce a conductivity path lower than that through the solution. If such deposits are present, the only way of getting rid of them is by soaking the cell in deionized water. 7.Ensure the correct temperature is selected for the operating procedures being used (if possible). 8.Follow instructions Page 33-36 for correct measurement. 8

9. Your Tasks – …in Groups of Not More than 5 Students 1- Calibrate the conductivity meter: Prepare 100 ml 0.01 M aqueous solution of potassium chloride from the provided stock concentration (3M). Do the required calculation. 2- Prepare and measure the conductivity of the following: 1-deionized water2- ultrapure water3- tap water 4- one nonprotic organic solvent of your choice 5- one beverage of your choice 6- one aqueous solution of an organic compound prepared by you (250 ml), prepare any concentration that does not exceed a 50 mg / L. 7- one aqueous solution of an inorganic compound prepared by you (250 ml), prepare any concentration that does not exceed a 50 mg / L. 9

10.  Example of a results table: sample disodium schnaffat pulaminol Deionized H 2 O … (Real T.D.S) concentration [mg L -1 ] 18 mg/L50 mg/L…… conductivity reading [  S cm -1 or mS cm -1 ] 120  S / cm62.5  S / cm2.2  S / cm … T.D.S. reading [mg L -1 or g L -1 ] 20 mg / L37.5 mg / L1.4 mg / L… Real TDS reading/ EC ratio 0.150.80n/a…  Hints for you lab report: - Show you calculations, - Copy your cell constant - Answer questions in the lab manual. 10

11. Assessment Brief description 4 marks Calculations3 marks Final statement 1 mark Questions 2 marks 11